Enoden Umi No Mieru Tabi Set

so I opened the motor and found out that one of the little cog wheels in the motor was slightly cracked....

That doesn't mean that it was not BNIB. The plastic cogs can crack with age / storage conditions as well as mis-use (the Benkei / Western Steamer engine unit is notorious for this - I have one with FIVE cracked or split gears in it, I must have a chat with Ripley802 about getting some replacements sometime). There are a number of threads on BPT (and Youtube videos) dealing with the replacement of split gears, and you can buy the commoner sizes new on Ebay or Alibaba so you don't need to cannibalise other engines.

Please note that the year written on the parts do not indicate the year of manufacture.

Nor does the country of manufacture written on the parts necessarily mean that that's where they were made, since it would presumably be easy for Tomy to move moulds from one production plant to another.